Breeding Dogs for Profit is Controversial > 자유게시판

­The relationship between people and dogs goes back at least 15,000 years, making dogs potentially the first animal to be domesticated. In that time, dogs have played many roles and performed many jobs for their human companions. Dogs come in a startling variety of shapes and sizes, but from the giant and noble Great Dane to the tiny and tenacious Chihuahua, they are all one species with one basic history. In this article, we'll explore where dogs came from and why they look and act the way they do. We'll also learn what recent genetic work has to tell us about our dogs and talk about how to find the right dog for you. Canids are part of a larger group called Carnivora, which also includes bears, cats and seals. Fossils show us that Canidae split off from the common ancestors of Carnivora about 40 million years ago. From about 15 million years ago, we can subdivide Canidae into three subgroups: fox-like animals, wolf-like animals and South American canids, such as the maned wolf and crab-eating fox.

Members of the wolf-like group include wolves, coyotes and jackals, which are all closely related. Observing the diversity of dogs and wild canids, scientists like Charles Darwin reasoned that different types of dogs might be descended from different types of wild canids. However, modern DNA analysis shows us that dogs are descended only from wolves. In the next section, we'll look at how this evolution might have happened. The conventional view, and one widely represented in both fiction and nonfiction, is that prehistoric people took wolf pups from their dens and reared them to think of people as their "pack." These tamed wolves lived with people and reproduced. The people that cared for them treasured individuals with odd coats or heavier bone structure, which might have meant death in the wild. Over time people began to breed these wolf-dogs selectively until they eventually created the diversity of dogs we see today.

The problem with this theory is that the initial shift from wolf-like to dog-like traits could only have happened very slowly. Wolves are relatively uniform in appearance, so the odds of a mutation appearing randomly in a captive population are small. It would have taken many thousands or even millions of years to get much diversity. Yet fossil evidence shows that dogs appeared not all that long ago. If it's true that dogs have existed for only about 15,000 years, this is a blink of the eye in evolutionary terms. DNA evidence indicates that dogs may have begun to split with wolves as many as 100,000 years ago, but this is still relatively recent. Yet in dogs we see some of the most extreme physical diversity of any mammalian species. There is more variation in size, color, coat texture and other aspects of appearance within dogs than there is among all other members of the canid family.

Recent publications, such as the controversial book "Dogs: A Startling New Understanding of Canine Origin, Behavior, & Evolution," by Raymond and Lorna Coppinger, present an alternative theory for the way that dogs evolved from wolves. The Coppingers suggest that some wolves "domesticated themselves." When humans went from mobile hunter/gatherer societies to sedentary villagers, they created a new ecological niche for neighboring wolves. The traditional niche for wolves is a forest predator of herbivores (plant-eaters) such as deer and elk. This niche requires wolves to be large, strong, increase testosterone innovative and able to learn by example. Humans living together in a group produce food scraps and other waste, which represents a valuable food source for animals. Wolves living near people began taking advantage of these resources, and the boldest wolves got the most and survived the best. Studies with captive wolves demonstrate that while you can raise wolves to be somewhat tolerant of people, they retain a suspicious nature and are extremely difficult to train.